Release snap only when its files are modified

[abitrolly]

Right now every commit releases new snap at https://snapcraft.io/yakshaveinc That creates unnecessary flow of update downloads. The solution is to build and deploy only when modifications touch files related to specific snap.

The should help

CHANGED_FILES=($(git diff --name-only $TRAVIS_COMMIT_RANGE))

https://stackoverflow.com/questions/38549616/travis-determine-which-files-changed

[abitrolly]

There is a problem with this approach. If the previous build fails, or has been skipped, the won't be any releases on subsequent commits. For example:

1. The commit modifies both top level .travis.yml and snap/snapcraft.yaml
2. The build fails because of error in .travis.yml
3. The next commit fixes .travis.yml, but rebuild of snap is not triggered, because snap/snapcraft.yaml was not touched

Another solution to the problem of unnecessary flow of updates is to build snaps always, in reproducible way, and upload only if the built snap changes.

[abitrolly]

See #39.

[abitrolly]

See also https://dev.to/ahferroin7/skip-ci-stages-in-travis-based-on-what-files-changed-3a4k